U.S. patent application number 16/221954 was filed with the patent office on 2019-04-25 for system and method for cryogenic cooling.
The applicant listed for this patent is Brooks Automation, Inc.. Invention is credited to Allen J. Bartlett, Mark Collins, Michael J. Eacobacci, William Johnson, James A. O'Neil, Sergei Syssoev.
Application Number | 20190120528 16/221954 |
Document ID | / |
Family ID | 44515101 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190120528 |
Kind Code |
A1 |
Bartlett; Allen J. ; et
al. |
April 25, 2019 |
System and Method for Cryogenic Cooling
Abstract
A heat exchanger within an insulated enclosure receives primary
refrigerant at a high pressure and cools the primary refrigerant
using a secondary refrigerant from a secondary refrigeration
system. An expansion unit within the insulated enclosure receives
the primary refrigerant at the high pressure from the heat
exchanger and discharges the primary refrigerant at a low pressure.
A supply line delivers the primary refrigerant at the low pressure
to the load and a return line returns the primary refrigerant from
the load to the primary refrigeration system. A system control unit
controls operation of at least one of the primary refrigeration
system and the secondary refrigeration system to provide a variable
refrigeration capacity to the load based on at least one of: a
pressure of the primary refrigerant delivered to the load, and at
least one temperature of the load.
Inventors: |
Bartlett; Allen J.; (New
London, NH) ; Johnson; William; (Andover, MA)
; Collins; Mark; (Plymouth, MA) ; Syssoev;
Sergei; (Townsend, MA) ; O'Neil; James A.;
(Bedford, MA) ; Eacobacci; Michael J.;
(Dennisport, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brooks Automation, Inc. |
Chelmsford |
MA |
US |
|
|
Family ID: |
44515101 |
Appl. No.: |
16/221954 |
Filed: |
December 17, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13106180 |
May 12, 2011 |
10156386 |
|
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16221954 |
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61363514 |
Jul 12, 2010 |
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61333801 |
May 12, 2010 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 2600/0253 20130101;
F25B 2400/01 20130101; Y10T 279/34 20150115; F25B 9/006 20130101;
F25B 2700/21 20130101; Y02B 30/70 20130101; F25B 2400/06 20130101;
F25B 2600/0251 20130101; F25B 9/02 20130101; F25B 7/00 20130101;
Y02B 30/741 20130101; F25B 9/14 20130101; F25B 9/002 20130101 |
International
Class: |
F25B 7/00 20060101
F25B007/00; F25B 9/02 20060101 F25B009/02; F25B 9/14 20060101
F25B009/14; F25B 9/00 20060101 F25B009/00 |
Claims
1. A system for providing a cooling refrigerant to a load, the
system comprising: a closed loop primary refrigeration system
comprising a compressor taking in the refrigerant at a low pressure
and discharging the refrigerant at a high pressure; an expansion
valve receiving the refrigerant at the high pressure from the
compressor and discharging the refrigerant at the low pressure to
an insulated enclosure, the insulated enclosure comprising an inlet
receiving the refrigerant from the expansion valve and an outlet
returning the refrigerant at the low pressure to the compressor; at
least one heat exchanger within the insulated enclosure receiving
the refrigerant at the low pressure and cooling the refrigerant
using a secondary refrigeration system in heat exchange
relationship with the refrigerant; a supply line delivering the
refrigerant at the low pressure to the load and a return line
returning the refrigerant from the load to the primary
refrigeration system; the secondary refrigeration system, wherein
the secondary refrigeration system comprises at least one secondary
cryogenic refrigerator; and a system control unit controlling
operation of at least one of the primary refrigeration system and
the secondary refrigeration system to provide a variable
refrigeration capacity to the load based on at least one of: a
pressure of the primary refrigerant delivered to the load, and at
least one temperature of the load.
2. The system of claim 1, the system control unit controlling
operation of the secondary refrigeration system to avoid either
undercooling of the load or overcooling of the load, based on (i) a
measured pressure or a measured temperature of the primary
refrigerant returned from the load that is cooled by the primary
refrigerant or (ii) a measured pressure or a measured temperature
of the primary refrigerant entering the load that is cooled by the
primary refrigerant.
3. The system of claim 1, further comprising a first channel of the
secondary refrigeration system delivering cooling from the
secondary refrigeration system to at least one heat transfer
surface of the load, and a second channel of the secondary
refrigeration system delivering the secondary refrigerant to the at
least one heat exchanger.
4. The system of claim 1, the system control unit controlling at
least one of a high pressure, a low pressure and a pressure
differential of the primary compressor.
5. The system of claim 1, the system control unit controlling a
heat source to supply heat to be delivered to the primary
refrigerant or controlling a heat source to supply heat to be
delivered to the secondary refrigerant.
6. The system of claim 1, wherein the expansion unit comprises an
adjustable throttle, the system control unit controlling operation
of the adjustable throttle.
7. The system of claim 1, the system control unit controlling flow
of the primary refrigerant to bypass at least a portion of the at
least one heat exchanger or at least a portion of the primary
refrigeration system.
8. The system of claim 1, the system control unit controlling a
rate of flow of the primary refrigerant or controlling a rate of
flow of the secondary refrigerant.
9. The system of claim 1, the system control unit controlling a set
point temperature of the secondary refrigeration system or
controlling a speed of a secondary compressor of the secondary
refrigeration system.
10. The system of claim 1, the system control unit controlling flow
of the secondary refrigerant to bypass at least a portion of the
secondary refrigeration system.
11. The system of claim 1, the system control unit controlling flow
of at least a portion of the primary refrigerant to warm at least a
portion of the load or controlling flow of at least a portion of
the secondary refrigerant to warm at least a portion of the
load.
12. The system of claim 1, comprising a transfer line out of the
insulated enclosure delivering the refrigerant at the low pressure
to the load, the transfer line returning the refrigerant from the
load to the insulated enclosure.
13. The system of claim 1, wherein the load is within the insulated
enclosure.
14. The system of claim 1, wherein the load comprises at least one
of: a semiconductor substrate, a fluid stream for cryogenic
separation, a gas to be liquefied, a biological sample, a chemical
process, material property analysis equipment, a water vapor trap,
an article in a manufacturing process, an imaging device, a
subatomic particle detector, a photonic detector, chemical analysis
equipment, a superconducting cable, and a superconducting
device.
15. The system of claim 1, wherein the secondary refrigeration
system comprises a mixed gas refrigeration system.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 13/106,180, filed May 12, 2011, which claims the benefit of
U.S. Provisional Application No. 61/363,514, filed on Jul. 12,
2010; and claims the benefit of U.S. Provisional Application No.
61/333,801, filed on May 12, 2010. The entire teachings of the
above applications are incorporated herein by reference.
BACKGROUND
[0002] With continued miniaturization of semiconductor devices,
there has been an increased demand for ultra-shallow junctions. For
example, tremendous effort has been devoted to creating better
activated, shallower and more abrupt source-drain extension
junctions to meet the needs of modern semiconductor devices. It has
been discovered that very low wafer temperature during ion
implantation is advantageous for minimizing damage of a silicon
wafer. In addition, there is an ongoing need for very low
temperature cooling in a wide variety of other semiconductor
processes and other fields.
SUMMARY
[0003] In accordance with an embodiment of the invention, there is
provided a system for cooling a load. The system comprises a closed
loop primary refrigeration system comprising: a primary compressor
taking in a primary refrigerant at a low pressure and discharging
the primary refrigerant at a high pressure; an insulated enclosure
comprising an inlet receiving the primary refrigerant at the high
pressure from the primary compressor and an outlet returning the
primary refrigerant at the low pressure to the primary compressor;
at least one heat exchanger within the insulated enclosure
receiving the primary refrigerant at the high pressure and cooling
the primary refrigerant using a secondary refrigerant from a
secondary refrigeration system, the secondary refrigeration system
being in heat exchange relationship with the primary refrigerant in
the at least one heat exchanger; an expansion unit within the
insulated enclosure receiving the primary refrigerant at the high
pressure from the at least one heat exchanger and discharging the
primary refrigerant at the low pressure; and a supply line
delivering the primary refrigerant at the low pressure to the load
and a return line returning the primary refrigerant from the load
to the primary refrigeration system. The system further comprises
the secondary refrigeration system, which comprises at least one
secondary cryogenic refrigerator. A system control unit controls
operation of at least one of the primary refrigeration system and
the secondary refrigeration system to provide a variable
refrigeration capacity to the load based on at least one of: a
pressure of the primary refrigerant delivered to the load, and at
least one temperature of the load.
[0004] In further, related embodiments, the at least one
temperature of the load may comprise a temperature of from about
-80 C to about -250 C. The secondary refrigeration system may
comprise a first channel delivering cooling to at least one heat
transfer surface of the load and a second channel delivering the
secondary refrigerant to the at least one heat exchanger. The at
least one heat transfer surface may transfer heat to cool at least
a portion of the load to a temperature in the range of from about
-40 C to about -100 C. The at least one heat transfer surface may
comprise at least a portion of a chamber to receive a semiconductor
substrate to be processed by a system of the load. The secondary
refrigeration system may comprise a mixed gas refrigeration system.
The mixed gas refrigeration system may comprise more than one heat
exchanger and at least one phase separator. The secondary
refrigeration system may comprise a reverse Brayton refrigeration
system. The load may comprise at least one of a pre-cool cryogenic
interface module, a pre-cool chamber, a cold pad cryogenic
interface module, a platen, an electrostatic chuck and two separate
loads.
[0005] In other related embodiments, the system may further
comprise an electrical interface control unit in electronic
communication with the load. The electrical interface control unit
may receive an electronic signal indicating at least one
temperature of the load; and/or an electronic signal indicating at
least one set-point temperature of the load. The electrical
interface control unit may output an electrical signal to control
operation of the secondary refrigeration system to control at least
one temperature of the load. The at least one temperature of the
load controlled by the electrical interface control unit may
comprise a temperature of at least one heat transfer surface of the
load.
[0006] In further related embodiments, the system control unit may
comprise a control unit to control the providing of the variable
refrigeration capacity to the load based on at least the pressure
of the primary refrigerant delivered to the load; a control unit to
control a discharge rate of the primary compressor; a control unit
to control at least one of a high pressure, a low pressure and a
pressure differential of the primary compressor; a control unit to
control a heat source to supply heat to be delivered to the primary
refrigerant; a control unit to control operation of an adjustable
throttle; a control unit to control flow of the primary refrigerant
to bypass at least a portion of the at least one heat exchanger; a
control unit to control flow of the primary refrigerant to bypass
at least a portion of the primary refrigeration system; a control
unit to control a rate of flow of the primary refrigerant; a
control unit to control a rate of flow of the secondary
refrigerant; a control unit to control a set point temperature of
the secondary refrigeration system; a control unit to control a
heat source to supply heat to be delivered to the secondary
refrigerant; a control unit to control a speed of a secondary
compressor of the secondary refrigeration system; a control unit to
control flow of the secondary refrigerant to bypass at least a
portion of the secondary refrigeration system; a control unit to
control flow of at least a portion of the primary refrigerant to
warm at least a portion of the load; and/or a control unit to
control flow of at least a portion of the secondary refrigerant to
warm at least a portion of the load.
[0007] In further, related embodiments, the insulated enclosure may
be integrated into at least a portion of the secondary
refrigeration system. The at least one heat exchanger may comprise
a condenser. The system control unit may comprise a control unit to
adjust the speed of the at least one secondary cryogenic
refrigerator. The system control unit may further comprises a
control unit to adjust the speed of at least one secondary
compressor of the at least one secondary cryogenic refrigerator.
The system control unit may comprise a control unit to turn off at
least one of the at least one secondary cryogenic refrigerators.
The system control unit may control operation of at least one of
the primary refrigeration system and the secondary refrigeration
system to vary a proportion of the primary refrigerant that is
flowed to the load in a liquid phase versus a gaseous phase. The
system may comprise more than one secondary cryogenic refrigerator,
and the system control unit may comprise a control unit to control
operation of the more than one secondary cryogenic refrigerators to
run at different speeds from each other; or to run at the same
speed as each other. The system control unit may control operation
of at least one of the primary refrigeration system and the
secondary refrigeration system to maintain a substantially constant
temperature of the at least one temperature of the load. The system
control unit may comprise a control unit to route at least a
portion of the primary refrigerant to a warmer surface in the
system to reduce refrigeration applied to the load. The system
control unit may comprise a control unit to permit at least one of
variable speed operation of the primary compressor, and pulsed
operation of the primary compressor.
[0008] In further, related embodiments, the system control unit may
control operation of the secondary refrigeration system to avoid
undercooling of the load by: determining a calculated boiling point
of the primary refrigerant returned from the load based on a
measured pressure of the primary refrigerant returned from the
load; comparing a measured temperature of the primary refrigerant
returned from the load with the calculated boiling point; and, if
the measured temperature is more than a predetermined temperature
difference above the calculated boiling point, controlling the
secondary refrigeration system to increase available refrigeration
to the load. In another embodiment, the system control unit may
control operation of the secondary refrigeration system to avoid
undercooling of the load by: monitoring a temperature of the
primary refrigerant returning from the load at a first temperature
sensor downstream of the load; controlling a small heater,
downstream of the first temperature sensor, to turn on if the
temperature at the first temperature sensor has reached a
predetermined assumed saturation temperature point; monitoring a
temperature of the primary refrigerant at a second temperature
sensor, downstream of the small heater; and if the turning on of
the small heater raises the temperature of the primary refrigerant,
controlling the secondary refrigeration system to increase
available refrigeration to the load. In another embodiment, the
system control unit may control operation of the secondary
refrigeration system to avoid overcooling of the load by:
monitoring a temperature of the primary refrigerant returning from
the load at a first temperature sensor downstream of the load;
controlling a small heater, downstream of the first temperature
sensor, to turn on if the temperature at the first temperature
sensor has reached a predetermined assumed saturation temperature
point; monitoring a temperature of the primary refrigerant at a
second temperature sensor, downstream of the small heater; and if
the turning on of the small heater raises the temperature of the
primary refrigerant, determining the magnitude of the heat provided
by the small heater and, based on the magnitude, determining
whether to control the secondary refrigeration system to decrease
available refrigeration to the load. The system control unit may
comprise a control unit to adjust a variable heater on the at least
one secondary cryogenic refrigerator. The system control unit may
comprise a control unit to control a setpoint temperature of the at
least one secondary cryogenic refrigerator. The system control unit
may control more than one secondary cryogenic refrigerator to have
different setpoint temperatures from each other.
[0009] In further, related embodiments, the primary refrigerant may
comprise at least one of nitrogen, argon, xenon, krypton, helium or
a mixed gas refrigerant. The primary refrigerant may comprise at
least one refrigerant component having a boiling temperature that
is higher than a boiling temperature of a refrigerant used in the
secondary refrigeration system; such as, the primary refrigerant
may comprise at least one of argon, nitrogen, xenon and krypton,
and the secondary refrigerant may comprise at least one of helium
and neon. The primary refrigerant may comprise a refrigerant having
a boiling temperature that is lower than a boiling temperature of
at least one refrigerant used in the secondary refrigeration
system. The primary refrigerant may comprise at least one of argon,
nitrogen, xenon, krypton and helium, and the secondary refrigerant
may comprise a mixed gas refrigerant. The system may further
comprise a recuperative heat exchanger within the insulated
enclosure and exchanging heat between the primary refrigerant at
the high pressure flowing from the inlet of the insulated enclosure
and the primary refrigerant returned from the load, the
recuperative heat exchanger discharging the primary refrigerant at
the high pressure to a condenser. The system may further comprise a
bypass valve permitting bypassing of the recuperative heat
exchanger such that the primary refrigerant at the high pressure
flowing from the inlet of the insulated enclosure does not exchange
heat with the primary refrigerant returned from the load. The
system control unit may control operation of the secondary
refrigeration system to avoid undercooling of the load by:
monitoring a temperature in at least one of an intermediate point
in the recuperative heat exchanger and an end point of the
recuperative heat exchanger; and if the monitored temperature falls
below a predetermined temperature, controlling the secondary
refrigeration system to decrease available refrigeration to the
load.
[0010] In further, related embodiments, the load may comprise an
electrostatic chuck, which may be a portion of an ion implantation
system to manufacture a semiconductor device. The system may
further comprise a pre-cooling chamber to receive the semiconductor
device prior to its handling by the electrostatic chuck. The load
may comprise at least one of: at least a portion of a system for
cooling a semiconductor wafer, at least a portion of an ion
implantation system, and at least a portion of a physical vapor
deposition system. The at least one secondary cryogenic
refrigerator may comprise a Gifford-McMahon cycle refrigerator,
which may comprise a helium refrigerator. The at least one
secondary cryogenic refrigerator may comprise a pulse tube
refrigerator. The at least one secondary cryogenic refrigerator may
comprise at least one of a reverse Brayton cycle refrigerator, a
Stirling cycle refrigerator and a Joule-Thomson cycle refrigerator;
and may comprise a refrigerator using a single refrigerant or a
refrigerator using a mixed gas refrigerant. The at least one
secondary cryogenic refrigerator may comprise more than one
secondary cryogenic refrigerator connected to cool the primary
refrigerant in a parallel or series flow of the primary refrigerant
in heat exchange relationship with the more than one secondary
cryogenic refrigerators.
[0011] In further, related embodiments, the primary compressor of
the primary refrigeration system may comprise a variable speed
compressor. The system may further comprise a cryopumping surface
to create a vacuum within the insulated enclosure. The cryopumping
surface may comprise a second stage of cooling of the at least one
secondary cryogenic refrigerator. The system may further comprise a
bypass valve permitting the primary refrigerant to bypass the
supply line that delivers the primary refrigerant to the load and
the return line that returns the primary refrigerant from the load.
The expansion unit may comprise at least one of a capillary tube, a
valve with a variable flow area, a spring biased valve, a piston
expander and a turbine expander. The system may further comprise a
pressure regulator regulating flow of the primary refrigerant
between a source of the primary refrigerant and the primary
refrigerant at the low pressure taken in by the primary compressor;
and a pressure control unit to control the pressure regulator to
regulate the flow of the primary refrigerant into the system. The
system may further comprise an isolation valve connected to a
pressure gauge on the insulated enclosure, the isolation valve
preventing flow of the primary refrigerant into the inlet of the
insulated enclosure if the pressure gauge on the insulated
enclosure detects a pressure above a predetermined maximum safe
pressure. The system may further comprise a thermal sensor
connected to monitor the temperature of the primary refrigerant
returning from the insulated enclosure to the primary compressor;
and a safety control unit connected to discontinue operation of the
secondary refrigeration system if the temperature of the primary
refrigerant returning from the insulated enclosure is less than a
predetermined touch hazard minimum temperature. The system may
further comprise a purifier removing impurities from gas directed
from a supply source of the primary refrigerant, prior to the
primary refrigerant entering the system; and/or an oil separator
removing oil from the primary refrigerant within the primary
compressor. At least a portion of each of the supply line and the
return line may extend within a vacuum insulated transfer line. The
at least one heat exchanger may convert at least a substantial
portion of the primary refrigerant to a liquid phase; or the at
least one heat exchanger may substantially not convert the primary
refrigerant to a liquid phase. The expansion unit may convert at
least a substantial portion of the primary refrigerant to a liquid
phase.
[0012] In further, related embodiments, the supply line may deliver
the refrigerant at the low pressure to the load through a transfer
line out of the insulated enclosure, and the return line may return
the refrigerant from the load to the insulated enclosure through
the transfer line. The load may be within the insulated enclosure.
The load may comprise at least one of: a semiconductor substrate, a
fluid stream for cryogenic separation, a gas to be liquefied, a
biological sample, a chemical process, material property analysis
equipment, a water vapor trap, an article in a manufacturing
process, an imaging device, a subatomic particle detector, a
photonic detector, chemical analysis equipment, a superconducting
cable, and a superconducting device.
[0013] In another embodiment according to the invention, there is
provided a system for providing a cooling refrigerant to a load.
The system comprises a closed loop primary refrigeration system
comprising a compressor taking in the refrigerant at a low pressure
and discharging the refrigerant at a high pressure; an expansion
valve receiving the refrigerant at the high pressure from the
compressor and discharging the refrigerant at the low pressure to
an insulated enclosure, the insulated enclosure comprising an inlet
receiving the refrigerant from the expansion valve and an outlet
returning the refrigerant at the low pressure to the compressor; at
least one heat exchanger within the insulated enclosure receiving
the refrigerant at the low pressure and cooling the refrigerant
using a secondary refrigeration system in heat exchange
relationship with the refrigerant; and a supply line delivering the
refrigerant at the low pressure to the load and a return line
returning the refrigerant from the load to the primary
refrigeration system. The system further comprises the secondary
refrigeration system, which comprises at least one secondary
cryogenic refrigerator. A system control unit controls operation of
at least one of the primary refrigeration system and the secondary
refrigeration system to provide a variable refrigeration capacity
to the load based on at least one of: a pressure of the primary
refrigerant delivered to the load, and at least one temperature of
the load.
[0014] In another embodiment according to the invention, there is
provided a method for cooling a load. The method comprises
compressing a primary refrigerant in a primary compressor of a
closed loop primary refrigeration system, the primary compressor
taking in a primary refrigerant at a low pressure and discharging
the primary refrigerant at a high pressure; transferring the
primary refrigerant at the high pressure from the primary
compressor to an inlet of an insulated enclosure, and returning the
primary refrigerant at the low pressure from the insulated
enclosure to the primary compressor; transferring the primary
refrigerant at the high pressure to at least one heat exchanger
within the insulated enclosure, and cooling the primary refrigerant
in the at least one heat exchanger using heat exchange with a
secondary refrigerant from a secondary refrigeration system, the
secondary refrigeration system comprising at least one secondary
cryogenic refrigerator; expanding the primary refrigerant using an
expansion unit within the insulated enclosure, the expansion unit
receiving the primary refrigerant at the high pressure from the at
least one heat exchanger and discharging the primary refrigerant at
the low pressure; delivering the primary refrigerant at the low
pressure to the load and returning the primary refrigerant from the
load to the primary refrigeration system; and controlling operation
of at least one of the primary refrigeration system and the
secondary refrigeration system to provide a variable refrigeration
capacity to the load based on at least one of: a pressure of the
primary refrigerant delivered to the load, and at least one
temperature of the load.
[0015] In further, related embodiments, the method may further
comprise delivering cooling from the secondary refrigeration system
to at least one heat transfer surface of the load through a first
channel of the secondary refrigeration system, and delivering the
secondary refrigerant to the at least one heat exchanger through a
second channel of the secondary refrigeration system. The method
may further comprise controlling the providing of the variable
refrigeration capacity to the load based on at least the pressure
of the primary refrigerant delivered to the load. The method may
further comprise: controlling at least one of a high pressure, a
low pressure and a pressure differential of the primary compressor;
controlling a heat source to supply heat to be delivered to the
primary refrigerant; controlling operation of an adjustable
throttle; controlling flow of the primary refrigerant to bypass at
least a portion of the at least one heat exchanger; controlling
flow of the primary refrigerant to bypass at least a portion of the
primary refrigeration system; controlling a rate of flow of the
primary refrigerant; controlling a rate of flow of the secondary
refrigerant; controlling a set point temperature of the secondary
refrigeration system; controlling a heat source to supply heat to
be delivered to the secondary refrigerant; controlling a speed of a
secondary compressor of the secondary refrigeration system;
controlling flow of the secondary refrigerant to bypass at least a
portion of the secondary refrigeration system; controlling flow of
at least a portion of the primary refrigerant to warm at least a
portion of the load; and/or controlling flow of at least a portion
of the secondary refrigerant to warm at least a portion of the
load.
[0016] In further, related embodiments, the method may comprise
delivering the refrigerant at the low pressure to the load through
a transfer line out of the insulated enclosure, and returning the
refrigerant from the load to the insulated enclosure through the
transfer line. The load may be within the insulated enclosure. The
load may comprise at least one of: a semiconductor substrate, a
fluid stream for cryogenic separation, a gas to be liquefied, a
biological sample, a chemical process, material property analysis
equipment, a water vapor trap, an article in a manufacturing
process, an imaging device, a subatomic particle detector, a
photonic detector, chemical analysis equipment, a superconducting
cable, and a superconducting device. The method may further
comprise moving an object or fluid to be cooled from a heat
transfer surface of the load to another portion of the load.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The foregoing will be apparent from the following more
particular description of example embodiments of the invention, as
illustrated in the accompanying drawings in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, emphasis instead being
placed upon illustrating embodiments of the present invention.
[0018] FIG. 1 is a schematic diagram of a cooling system in
accordance with an embodiment of the invention.
[0019] FIG. 2 is a diagram of a thermal cycle of nitrogen gas in
accordance with an embodiment of the invention.
[0020] FIG. 3 is a schematic diagram of a cooling system using a
second stage cryogenic refrigerator as a cryopump, in accordance
with an embodiment of the invention.
[0021] FIG. 4 is a schematic diagram of a high throughput cooling
system in accordance with an embodiment of the invention.
[0022] FIG. 5 is a schematic diagram of a high throughput cooling
system with an insulated enclosure integrated into a mixed gas
refrigeration system, in accordance with an embodiment of the
invention.
DETAILED DESCRIPTION
[0023] A description of example embodiments follows.
[0024] In accordance with an embodiment of the invention, there is
provided a closed cycle cryogenic cooling source to provide a
solution for low-temperature ion implantation for use in
single-wafer high-throughput ion implanters. In addition, an
embodiment according to the invention may be used to provide
cooling in a wide variety of other possible applications, such as
to cool fluid streams for cryogenic separations, to liquefy gasses,
to provide cooling for biological freezers, control reaction rates
of chemical processes, to provide cooling for material property
analysis equipment, to trap water vapor to produce low vapor
pressures in vacuum processes, to cool articles in manufacturing
processes such as semiconductor wafer processing and inspection, to
cool imaging devices and other instrumentation, subatomic particle
and photonic detectors, to cool chemical analysis equipment and to
cool superconducting cables and devices. It will be appreciated
that the system may be used in other cooling applications.
[0025] FIG. 1 is a schematic diagram of a cooling system 100 in
accordance with an embodiment of the invention. In the embodiment
of FIG. 1, the system 100 uses cryogenic refrigerators 101/102/103
to cool a recirculating refrigerant, such as a nitrogen stream 104.
With reference to the thermal diagram of FIG. 2 in which parallel
numbering is used to the components of FIG. 1, the nitrogen is
pre-cooled 205a/b in first and second portions 105a/b of a
recuperative heat exchanger 105 (which may alternatively be
implemented as two separate heat exchangers), condensed 206 using
cryogenic refrigerators 101/102/103, expanded 207 using expansion
unit 107 (at least a portion of the refrigerant may be changed from
a gas state to a liquid state by the cryogenic refrigerators
101/102/103, and/or by the expansion unit 107), and provided 208 to
the load 108 where the nitrogen boils, extracting heat to cool the
load 108, and returns to the system in gas form. The returned
nitrogen is warmed by returning 205a/b through the recuperative
heat exchanger 105a/b, while pre-cooling 205a/b the incoming stream
by heat exchange between the returning stream and the incoming
stream within the recuperative heat exchanger 105a/b. The nitrogen
then returns to be recompressed 209 in the compressor package 109.
The system 100 may be used for providing cooling to a wafer chuck
used in ion implantation during the semiconductor fabrication
process, as well as for other applications noted above.
[0026] In the embodiment of FIG. 1, the system includes a cryogenic
refrigeration system 101/102/103, a nitrogen compressor 109, an
insulated enclosure 110 (where heat transfer from the refrigerators
101/102/103 to the recirculating nitrogen stream 104 occurs),
valving, flow controls, pressure controls, safety controls, system
controls, and purification (all discussed further below). Instead
of a recirculating nitrogen stream 104, the system may use a stream
of argon, xenon, krypton, another pure refrigerant, a mixed
refrigerant, or any refrigerant (such as nitrogen and/or argon)
comprising a refrigerant component that boils at a temperature
warmer than the boiling point of the refrigerant used in
refrigerators 101/102/103. It should be appreciated that as used
herein a "refrigerant" may be a mixture of a gaseous and a liquid
phase, and the ratio of gas to liquid may change over the course of
a refrigeration cycle. The cryogenic refrigeration system
101/102/103 uses helium as the refrigerant through one or more
refrigerators 101/102/103 running a Gifford-McMahon (GM)
refrigeration cycle. Alternately, a reverse Brayton cycle, a
Stirling cycle or a Joule Thomson expansion cycle with either
single or mixed refrigerant may be used to provide refrigeration
101/102/103. Instead of helium, the cryogenic refrigeration system
101/102/103 may use a refrigerant comprising another cold boiling
refrigerant component, such as neon. One embodiment uses multiple
refrigerators 101/102/103, which may be in series or parallel,
although a single refrigerator is also possible.
[0027] In the embodiment of FIG. 1, the nitrogen compressor 109
uses a hermetically sealed rotary vane pump modified for
compressing dry gases; however, a scroll or any other type of pump
could also be used. The pump may operate at a variable speed.
Alternatively, a constant speed pump may be used. In order to
manage the heat of compression, oil may be injected into the
nitrogen stream before or during compression by compressor 109.
This oil is then removed from the nitrogen stream though an oil
separator 135 consisting of a dense pack of fiberglass and a room
temperature adsorber with activated charcoal.
[0028] In the embodiment of FIG. 1, the insulated enclosure 110 is
achieved through creating a low pressure or vacuum envelope around
the components that will be below room temperature. The insulating
vacuum may be provided by a turbo molecular pump 111, backed by a
diaphragm roughing pump 112, but can also be created through
cryopumping. For example, a second stage cryogenic refrigerator 313
(see FIG. 3), or another cryogenic refrigerator, could be used as a
cryopump to create the vacuum within the enclosure 110. Insulating
vacuum is also used along the thermally isolated transfer line 114
carrying the liquid nitrogen to the load 108 to be cooled, either
by using a rigid transfer line open to the vacuum space of the
insulated enclosure 110, vacuum jacketed bayonette fittings, or by
a separately sealed vacuum space along the transfer line 114,
either actively pumped or initially brought to a low pressure and
sealed. The insulation can also be achieved through other
insulation systems such as foam around the cold components.
[0029] In the embodiment of FIG. 1, the heat transfer out of the
nitrogen into the cryogenic refrigerators 101/102/103 is achieved
through direct thermal conduction from the refrigerator 101/102/103
to a mass of copper around which is wound a tubular heat exchanger.
The copper mass may be part of the refrigerator or may be joined to
the refrigerator in a manner that enables thermal conduction. The
copper mass may have a helical scalloped groove to support the
tube, which is brazed in place to maximize thermal transfer.
Alternately, a D-shaped tube, with a flat on one side, can be used.
The tube has a smooth inner diameter, but internal fins, grooves,
or a rough finish can be used to increase the internal surface area
and improve thermal transfer.
[0030] In the embodiment of FIG. 1, the valving comprises two
isolation valves 115/116, one 115 on the line supplying liquid
nitrogen to the load and one 116 on the line returning the nitrogen
boil-off, and a bypass valve 117 which allows the liquid nitrogen
to circulate without being sent to the load 108. The valving
115/116/117 allows a mode of operation where the system can be
pre-cooled to operating temperatures before refrigeration is
applied to the load 108 and the system can be maintained at low
temperatures during periods of time where refrigeration is not
required at the load 108. The valves can have a thermally isolated
actuation device, whether manual, pneumatic, or electrical, which
minimizes the heat leak from the valves to the external
environment. The thermal isolation is achieved through thin wall
tubes, with our without cut-outs which can further reduce the cross
sectional area between the valve body and the actuation device.
Thermal isolation can also be achieved through the use of materials
with low thermal conductivities.
[0031] In the embodiment of FIG. 1, flow control may be achieved
through the use of a capillary tube 107 explicitly sized for the
temperatures, pressures, percent of liquid saturation, and desired
flow of the system. The capillary 107 is placed between the
refrigerators 101/102/103 and the line 114 supplying liquid
nitrogen to the load, but the location can be varied in the system.
Alternate methods of flow control include a warm throttle valve or
other expansion valve which switches in an orifice between the
compressor 109 and the warm heat exchanger 105, a valve with a
variable flow area, a spring biased valve, or by varying the speed
of the compressor 109.
[0032] In the embodiment of FIG. 1, a semiconductor device that is
being manufactured may be pre-cooled to reduce the required cooling
refrigerant at the electrostatic chuck. For example, a flow line
(not shown) may divert nitrogen from a location in nitrogen loop
104 to a pre-cooling chamber (not shown).
[0033] In the embodiment of FIG. 1, pressure control is provided by
a pressure regulator 118 between a source of nitrogen and the
return side of the nitrogen compressor, a high side pressure
control valve 119, a bypass regulator 120, and the speed of the
compressor 109. The pressure regulator 118 allows gas to be drawn
from the source of nitrogen to compensate for the volume difference
between gaseous and liquid nitrogen and maintain pressure as the
nitrogen is being condensed and therefore controls the minimum
pressure for the return side of the nitrogen compressor. The
nitrogen source could be either from a high pressure cylinder, the
facility nitrogen source in the semiconductor fabrication plant or
a local nitrogen generator. The pressure regulator 118 is set to a
constant value, but could also be actively controlled by a pressure
control unit 136 to modify the gas flow into the system which would
allow the temperature at which refrigeration is applied to the load
108 to be varied dynamically. The high side pressure control valve
119 limits the supply side pressure when the nitrogen in the system
is boiling off, either under conditions of increasing load, or when
the system is being shut down. The bypass regulator 120 is placed
between the high pressure side and low pressure side of the
nitrogen compressor 109 and controls the power required by the
compressor 109 and, in conjunction with the high side pressure
control valve 119, the maximum pressure of the return side of the
compressor 109. The compressor speed and the pressure regulator
setting define the minimum pressure of the supply side of the
compressor 109. The speed of the compressor 109 may be varied.
Alternatively, the speed of the compressor 109 may be constant.
[0034] In the embodiment of FIG. 1, safety controls are provided
through relief valves 119/121/122/123/124 on the nitrogen lines and
insulated enclosure 110 and a relief valve on the compressor 109,
isolation valves 125/126 on the nitrogen stream, and a thermal
sensor 137. The relief valves 119/121/122/124 on the nitrogen lines
are installed on any volume that could be potentially isolated
through operation of the valves or disconnection of the lines
carrying nitrogen from the compressor 109 to the insulated
enclosure 110. The relief valve 123 on the vacuum space 110 is
sized to prevent over pressurization of the enclosure 110 in the
event of a nitrogen line break and subsequent boil-off within the
enclosure 110. The isolation valve 125 on the nitrogen stream is
controlled by a pressure gauge 127 on the insulating enclosure 110.
If the gauge 127 senses a high pressure, such as above 1 micron, a
relay on the gauge 127 trips, cutting power to the isolation valve
125 which is a normally closed configuration and which therefore
closes. This prevents nitrogen from the source of supply from
continuing to enter the enclosure 110 in case of a nitrogen line
break or vacuum leak which would lead to evaporation of liquid
nitrogen in the nitrogen lines. A thermal sensor 137 monitors the
temperature of the nitrogen leaving the insulated enclosure 110 to
return to compressor 109 and will stop operation of the
refrigerators 101/102/103 (or reduce refrigeration provided by
them) if the temperature is low enough to create a touch
hazard.
[0035] In the embodiment of FIG. 1, the system control unit 139
includes one or more control units configured to adjust the amount
of refrigeration power available to avoid either overcooling or
undercooling the system, allowing the system to provide the proper
amount of refrigeration to the load 108 without creating a
hazardous situation. Further operation of the control units that
are implemented by system control unit 139 is discussed below. It
will be appreciated that system control unit 139 is electrically
connected to various sensors and devices discussed herein,
including sensors 130, 131, 133, 137, small heater 132, compressors
109 and 128, and other sensors and devices as necessary to control
operation of the system as described herein. The system control
unit 139 includes appropriate electronic hardware, including
specially programmed microprocessors or other specially programmed
electronics to implement the control techniques described herein.
Further, it will be appreciated that where a "control unit" is
discussed herein it may be implemented as a subunit of the system
control unit 139, such as by a subroutine or subcomponent of a
microprocessor or other electronic hardware of the system control
unit 139. In order to prevent overcooling or undercooling, the
system control unit 139 adjusts the speed of the cryogenic
refrigerators 101/102/103 and/or helium compressor 128 and/or turns
off one or more of the refrigerator units 101/102/103. This results
in a change in the percent of the flow to the load 108 that is in
liquid phase, as opposed to gaseous phase. In normal operation,
i.e., not overcooled or undercooled, the refrigerators 101/102/103
are allowed to run at different speeds, although they could also be
constrained to all run at the same speed to balance the
refrigeration load across all refrigerators. It should also be
appreciated that one or more of the cryogenic refrigerators
101/102/103 may be of different sizes or different refrigeration
types, or all of the cryogenic refrigerators may be the same size
and refrigeration type. In addition, the control units may provide
the cryogenic refrigerators 101/102/103 with control parameters
(such as a maximum or minimum refrigerator speed) within which the
cryogenic refrigerators must run, while allowing the cryogenic
refrigerators to perform local control (using one or more on-board
local processors) within the maximum and minimum parameters.
Further, the control units may control the setpoint temperature of
the refrigerators 101/102/103 directly, rather than controlling
speed of the refrigerators directly. The refrigerators 101/102/103
may be controlled to have different setpoint temperatures.
[0036] In the embodiment of FIG. 1, other options exist to adjust
the available refrigeration. For instance, a variable heater 140
could be used to reduce the amount of refrigeration applied by
cryogenic refrigerators 101/102/103 running at either a constant or
variable speed. Another method would be to use a valve to route the
nitrogen flow around the return side heat exchanger 105b,
preventing or allowing precooling of the incoming nitrogen before
it reaches the cryogenic refrigerators 101/102/103. A portion of
the flow could also be routed to a warmer surface in the system to
reduce the refrigeration applied to the load 108. The available
refrigeration could also be adjusted by changing the flow in the
nitrogen stream with either a variable speed compressor 109 or by
pulsing the flow by turning a constant speed compressor on and
off.
[0037] In the embodiment of FIG. 1, for the system controls to be
effective, the system may be able to detect both under-refrigerated
and over-refrigerated conditions. Detection of under refrigeration
may be done by measuring the pressure on the return line of the
nitrogen circuit using a pressure transducer 130, which determines
the boiling point of the liquid nitrogen, which is then calculated.
Data from a temperature sensor 131 on the return line is then
compared with the calculated value. If the measured temperature is
more than a preset temperature difference above the calculated
temperature, it is an indication that the system is not returning
liquid or near liquid nitrogen from the load 108 and can make use
of more refrigeration. The refrigerators 101/102/103 are then
commanded to increase their available refrigeration through means
such as increasing their speed. The detection of an
under-refrigerated condition can be also achieved through other
means, such as a complete model of the thermodynamic system and
comparing system parameters such as inlet and outlet temperatures,
inlet and outlet pressures, and flows. Another method is to monitor
the return temperature using temperature sensor 131 and, when it
reaches an assumed saturation temperature point, turn on a small
heater 132 downstream of temperature sensor 131. A second
temperature sensor 133 downstream of the small heater 132 is then
monitored to see if the addition of the small amount of heat raised
the temperature of the nitrogen. If it did, the nitrogen stream is
exceeding a set level of superheat and more refrigeration is
needed.
[0038] In the embodiment of FIG. 1, detection of over-refrigeration
is important for safety and potentially energy efficiency reasons.
Over-refrigeration may be monitored by looking at the temperature
at an intermediate point through the recuperative heat exchanger
105a/b, or alternately at either end. If this temperature falls
below a pre-set level, the system adjusts to reduce available
refrigeration. A secondary control thermal sensor 137 monitors the
temperature of the nitrogen leaving the heat exchangers 105a/b and
returning to the compressor 109. If this value falls below a
temperature considered to be a touch hazard, all refrigerators
101/102/103 are disabled by a safety control unit 138 and the
system operation is locked out. Another method is to monitor the
return temperature using a temperature sensor 131 and, when it
reaches an assumed saturation temperature point, turn on a small
heater 132 downstream of the point 116 where the temperature sensor
131. A second temperature sensor 133 downstream of the small heater
132 is then monitored to see if the addition of the small amount of
heat raised the temperature of the nitrogen. The magnitude of the
amount of heat needed to raise the temperature is an indicator of
whether there is over-refrigeration. In addition, temperatures at
specific locations such as at the load may be used for feedback
control of increasing or decreasing refrigeration to the load.
Decreasing refrigeration to the load may be accomplished by
reducing the refrigeration produced by refrigerators 101/102/103
and/or by diverting flow from the load through bypass valve
117.
[0039] In addition, in an embodiment according to the invention in
which there is two-phase flow of the refrigerant (i.e., the
refrigerant includes a liquid and a gaseous phase), the system
control unit 139 may regulate the temperature of the load using
information regarding the pressure of the refrigerant entering the
load (i.e., refrigerant inlet pressure to the load), and without
the need to receive temperature feedback. This is possible because
of the pressure/temperature relationship of a two-phase mixture. In
one embodiment, both the inlet pressure and a downstream
temperature of the load may be used to permit the system control
unit 139 to regulate the temperature of the load; in another
embodiment, only the inlet pressure may be used. Where control
techniques are described herein as being based on one or more
temperatures, similar techniques may therefore also be used based
on pressure and temperature or only on pressure.
[0040] In the embodiment of FIG. 1, purity of the recirculating
nitrogen may be ensured through several methods in the system.
First, the gas from the source of nitrogen supply outside of the
system is passed through a purifier 134 using either heated or
un-heated getter material to remove impurities. Within the nitrogen
compressor 109, the oil introduced into the nitrogen stream is
removed though an oil separator 135 consisting of a dense pack of
fiberglass and a room temperature adsorber with activated charcoal,
which also removes water and other gaseous contaminants. Finally,
the nitrogen stream is passed through a cold adsorber 129 within
the insulated enclosure 110. Care is taken to reduce the
introduction of contaminants in the use of the system as well.
Isolation valve 126 may allow for room temperature or heated
nitrogen to be introduced into the system to warm the load, and
pressure regulator 118 may be used to ensure that positive pressure
is always maintained within the nitrogen stream.
[0041] FIG. 4 is a schematic diagram of a high throughput cooling
system 400 in accordance with an embodiment of the invention. In
the embodiment of FIG. 4, the system 400 uses a dual channel mixed
gas refrigerant system 441 to permit pre-cooling of a substrate to
be cooled, in addition to cooling a recirculating refrigerant such
as a nitrogen stream 404. The cooling system 400 includes the mixed
gas refrigerant system 441, a nitrogen recirculation compressor
409, an insulated enclosure 410, and an electrical interface
control box 442. The electrical interface control box 442 may be
separate from, or integral with, the electronics for controlling
the mixed gas refrigeration system 441. In the insulated enclosure
410, heat transfer from the mixed gas refrigeration system 441 to
the recirculating nitrogen stream 404 occurs. The insulated
enclosure 410 in the embodiment of FIG. 4 contains foam insulation,
although vacuum insulation as in the embodiment of FIG. 1 may be
used instead. The insulated enclosure 410 may include cold
components discussed below, which are insulated, while the nitrogen
compressor 409 is located outside of the insulated enclosure 410
and is at a warmer temperature, such as room temperature.
[0042] In the embodiment of FIG. 4, a first channel 443 of the
mixed gas refrigeration system 441 circulates mixed gas refrigerant
to pre-cooling equipment, for example to pre-cool a semiconductor
device that is being manufactured in order to reduce the required
cooling refrigerant at an electrostatic chuck. In FIG. 4, the first
channel 443 includes a first channel mixed gas refrigerant supply
line 444 to carry mixed gas refrigerant to the pre-cooling
equipment, and a first channel mixed gas refrigerant return line
445 to return the mixed gas refrigerant from the pre-cooling
equipment. The pre-cooling equipment may, for example, include a
pre-cool cryogenic interface module 446, which cools heat transfer
surfaces in one or more pre-cool chambers 447, 448; or the mixed
gas refrigerant may be circulated directly to the heat transfer
surfaces in pre-cool chambers 447, 448. In addition, the mixed gas
refrigerant may be circulated to any heat transfer surface in the
load, which may or may not be pre-cooling equipment and regardless
of whether pre-cooling equipment is used. Further, an embodiment
according to the invention may be used to cool two different loads
at two different temperatures, including where one of the loads is
not a pre-cool chamber for the other load. In addition to loads
such as semiconductor substrates discussed herein, any other load
may be cooled by an embodiment according to the invention. For
example, the load may include a fluid stream for cryogenic
separation, a gas to be liquefied, a biological freezer or other
biological sample, a chemical process, material property analysis
equipment, a water vapor trap for vacuum processes, an article in a
manufacturing process, an imaging device or other instrumentation,
a subatomic particle or photonic detector, chemical analysis
equipment or a superconducting cable or device. Other loads may be
cooled.
[0043] In accordance with one embodiment of the invention, the
pre-cool chambers 447, 448 may, for example, be used to cool
semiconductor substrates to a temperature in the range of from
about -40 C to about -100 C, after which the substrates may be
transferred to an electrostatic chuck 449 upon which ion
implantation or other processes are performed on the substrates. In
accordance with an embodiment of the invention, nitrogen directed
out of the insulated enclosures (such as 110 and 410) may, for
example, be used to achieve a target temperature of from about -80
C to about -250 C, such as from about -150 C to about -190 C, which
may be the temperature at a cold pad cryogenic interface module
465, a platen 466, an electrostatic chuck 449, or another location
at the load. By virtue of the pre-cooling of semiconductor
substrates in the pre-cool chambers 447, 448, an embodiment
according to the invention permits a higher throughput rate for the
semiconductor manufacturing equipment, because the semiconductor
substrates require less time to be cooled to a desired low
temperature at the electrostatic chuck 449 when the substrates have
already been pre-cooled in the pre-cool chambers 447, 448.
[0044] In the embodiment of FIG. 4, a second channel 450 of the
mixed gas refrigeration system 441 circulates mixed gas refrigerant
through heat exchangers contained within the insulated enclosure
410 in order to remove heat from a separate nitrogen gas loop 404
passing though a separate channel of the same heat exchangers. In
the embodiment of FIG. 4, the nitrogen loop 404 may circulate
essentially all of the nitrogen in a gaseous state throughout the
closed loop 404, although a mixture of liquid and gas may be
circulated as described above for the embodiment of FIG. 1. In the
nitrogen loop 404, the nitrogen is compressed by nitrogen
compressor 409 and delivered via nitrogen supply line 451 to one
side of a first heat exchanger 452, from which the nitrogen flows
to one side of a second heat exchanger 453. In the first and second
heat exchangers 452, 453, the nitrogen is cooled by nitrogen
returning from the load. After the second heat exchanger 453, the
nitrogen flows through an optional heater 454 to one side of a
third heat exchanger 455, from which the nitrogen flows to one side
of a fourth heat exchanger 456. In the third and fourth heat
exchangers 455, 456, the nitrogen is cooled by mixed gas
refrigerant (from the mixed gas refrigeration system 441), flowing
through the other sides of the third and fourth heat exchangers
455, 456. The nitrogen exits the fourth heat exchanger 456, flows
through an adsorber 457 to remove impurities, and is expanded
through an expansion unit, such as a capillary tube 458 or throttle
valve. The expansion unit is used to regulate the flow of the
nitrogen as well as to provide additional cooling through a gas
expansion effect. Following expansion, the nitrogen exits the
insulated enclosure 410 through nitrogen line 459 to cool the load,
and is returned from the load through return line 460 to the
insulated enclosure 410. The returning nitrogen is provided to the
other side of the second heat exchanger 453, and from there to the
other side of the first heat exchanger 452, in order to be warmed
and to cool the incoming nitrogen stream in the first and second
heat exchangers 452 and 453. From the first heat exchanger 452, the
nitrogen returns to the compressor 409 via return line 461 to be
compressed.
[0045] In this way, in the embodiment of FIG. 4, the first two heat
exchangers 452, 453 are used for recuperative heat exchange between
the cold nitrogen gas returning 460 from the load and the supply
gas 451 entering the insulated enclosure 410 from the nitrogen
compressor 409. The third and fourth heat exchangers 455, 456 are
used to transfer heat between the mixed gas refrigerant (from the
second channel 450 of the mixed gas refrigerant system 441), and
the nitrogen gas that has exited the first two heat exchangers. The
mixed gas refrigerant is supplied to the fourth heat exchanger 456
by mixed gas supply line 462 of the second channel 450 of the mixed
gas refrigeration system 441, is flowed through one side of each of
the fourth and third heat exchangers 456, 455, and from there
returns by mixed gas return line 463 of the second channel 450 to
the mixed gas refrigeration system 441. The heater 454 may be used
to prevent the mixed gas refrigerant from freezing in the heat
exchangers 455, 456.
[0046] In the embodiment of FIG. 4, the pressure difference between
the supply and return sides of the nitrogen compressor 409 (for
instance, the pressure difference between the nitrogen supply line
451 and the nitrogen return line 461), may be controlled in order
to achieve a desired nitrogen flow rate and expansion level as the
nitrogen is passed through the capillary tube 458. In addition, an
electronic inverter 464 may be used to reduce the speed of
compressor 409, in order to reduce the nitrogen flow rate exiting
the compressor 409.
[0047] In the embodiment of FIG. 4, valves 415/416/417 may be used
in a similar fashion to that described above for valves 115/116/117
of FIG. 1. In particular, the valving may comprise two valves
415/416, one 415 on the line supplying nitrogen to the load and one
416 on the line returning the nitrogen from the load, and a bypass
valve 417 which allows the nitrogen to circulate without being sent
to the load. The valving 415/416/417 allows a mode of operation
where the system can be pre-cooled to operating temperatures before
refrigeration is applied to the load and the system can be
maintained at low temperatures during periods of time where
refrigeration is not required at the load. The valves 415/416/417
need not be vacuum valves where the insulated enclosure 410 is not
vacuum insulated, although they may be so when vacuum insulation is
used.
[0048] The embodiment 400 of FIG. 4 may be used to interface with
equipment operated by an end-user for semiconductor fabrication or
other applications. For example, the customer equipment may include
one or all of a cold pad cryogenic interface module 465, a platen
466, an electrostatic chuck 449, a pre-cool cryogenic interface
module 446, and one or more pre-cool chambers 447, 448. The
nitrogen lines 459 and 460 exiting and returning to the insulated
enclosure 410 may be connected with such customer equipment, as may
be the mixed gas refrigerant supply and return lines 444 and 445.
The customer equipment may, for example, include the equipment
shown in portion 467 of FIG. 4.
[0049] In the embodiment of FIG. 4, an electrical interface control
box 442 provides an electrical interface between the customer
equipment 467, the mixed gas refrigeration system 441 and the
systems within the insulated enclosure 410. The electrical
interface control box 442 may for example, have as inputs or
outputs one or more of the following, or other electrical signals
regarding the state of such components: an input electronic signal
indicating a temperature at a remote location, such as the pre-cool
chambers 447, 448; an input electronic signal indicating a
temperature control set-point for the remote location such as
electrostatic chuck 449 or platen 466; an input electronic signal
indicating whether coolant is to flow from the first channel 443 of
the mixed gas refrigeration system 441; an input electronic signal
indicating whether coolant is to flow from the second channel 450
of the mixed gas refrigeration system 441; an output electronic
signal indicating cold is ready at the first channel 443 of the
mixed gas refrigeration system 441; an output electronic signal
indicating cold is ready at the second channel 450 of the mixed gas
refrigeration system 441; output electrical signals indicating the
temperatures of the supply and return nitrogen in lines 459 and
460; output electrical signals indicating the temperatures of the
mixed gas refrigerant supply and return lines 462 and 463; an
output electrical signal indicating a feedback for the mixed gas
refrigeration system 441; an output electrical signal indicating a
fault in one or more of the nitrogen loop 404 or either channel of
the mixed gas refrigeration system 441; an output electrical signal
indicating cold source power on. The electrical interface control
box 442 may be used to provide electrical control of one or more
systems or subsystems, for example to control operation of the
first channel 443 of the mixed gas refrigeration system 441 such
that a specified temperature is maintained at a remote point, such
as at one or more of the pre-cooling chambers 447 and 448. For
instance, the electrical interface control box 442 may pulse on and
off the operation of the first channel 443 of the mixed gas
refrigeration system 441 in order to control the temperature at
such a remote location. In addition to the electrical interface
control box 442, the embodiment of FIG. 4 includes a further system
control unit 439, which may be a separate unit connected with the
electrical interface control box 442 or may be integrated with it.
The system control unit 439 includes one or more control units 494
configured to adjust the amount of refrigeration power available to
avoid either overcooling or undercooling the system, allowing the
system to provide the proper amount of refrigeration to the loads
(including, for example, both the pre-cooling equipment 446/447/448
and cold pad cryogenic interface module 465) without creating a
hazardous situation. Further operation of the control units that
are implemented by system control unit 439 is discussed below. It
will be appreciated that system control unit 439 is electrically
connected to various sensors and devices discussed herein,
including heater 454, compressor 409, valves 415/416/417, and other
sensors and devices as necessary to control operation of the system
as described herein. The system control unit 439 includes
appropriate electronic hardware, including specially programmed
microprocessors or other specially programmed electronics to
implement the control techniques described herein. Further, it will
be appreciated that where a "control unit" is discussed herein it
may be implemented as a subunit of the system control unit 439,
such as by a subroutine or subcomponent of a microprocessor or
other electronic hardware of the system control unit 439.
[0050] In the embodiment of FIG. 4, the system control unit 439
controls the delivery temperatures to the load, including, for
example, any or all of the pre-cooling equipment 446/447/448, cold
pad cryogenic interface module 465, platen 466 and electrostatic
chuck 449. In order to control operation of the nitrogen loop 404
to control such delivery temperatures, several different possible
techniques may be used, either alone or in combination. In each
case, the system control unit 439 may receive a reading of one or
more temperatures at remote locations in the load, by receiving an
electronic signal from one or more temperature sensors (not shown),
and in response may control operation of one or more devices via
electronic signals to those devices, from one or more control units
used for such purposes. The system control unit 439 may therefore
implement a feedback loop to control delivery temperatures to the
load. The control may be continuous and closed loop, or
alternatively, the control may be open loop and need not be
continuous. In addition, in an embodiment according to the
invention in which there is two-phase flow of the refrigerant
(i.e., the refrigerant includes a liquid and a gaseous phase), the
system control unit 439 may regulate the temperature of the load
using information regarding the pressure of the refrigerant
entering the load (i.e., refrigerant inlet pressure to the load),
and without the need to receive temperature feedback. This is
possible because of the pressure/temperature relationship of a
two-phase mixture. In one embodiment, both the inlet pressure and a
downstream temperature of the load may be used to permit the system
control unit 139 to regulate the temperature of the load; in
another embodiment, only the inlet pressure may be used. Where
control techniques are described herein as being based on one or
more temperatures, similar techniques may therefore also be used
based on pressure and temperature or only on pressure.
[0051] In one example of control by the system control unit 439, in
the embodiment of FIG. 4, the discharge rate from the nitrogen
compressor 409 may be controlled by the system control unit 439 in
response to one or more temperatures at one or more remote
locations in the load. The speed of the nitrogen compressor 409 may
be varied, or the nitrogen compressor 409 may be turned on and off,
by the system control unit 439. The system control unit 439 may
control the high pressure (supply pressure) of the nitrogen
compressor 409, for example the pressure at nitrogen supply line
451. Further, the system control unit 439 may control the low
pressure (return pressure) of the nitrogen compressor 409, for
example the pressure at nitrogen return line 461. Further, the
system control unit 439 may control the pressure differential
between the high pressure and the low pressure of the nitrogen
compressor 409; or may control two or more of the pressure
differential, the high pressure and the low pressure of the
nitrogen compressor 409. The system control unit 439 may control
the heat supplied to the flowing nitrogen loop 404, for example
using an electronic signal to heater 454, another heater, or
another heat source. The system control unit 439 may use an
electronic signal to control an adjustable throttle, which would be
used in place of capillary tube 458. The system control unit 439
may use an electronic signal to switch flow (for example by
providing electronic signals to one or more valves) through a hot
gas bypass (not shown) in the nitrogen loop 404, for example, to
direct flow of the nitrogen to bypass some portions (or all of) of
one or more of the heat exchangers 452, 453, 455, 456, resulting in
short-circuiting of the cooling loop for the nitrogen. The system
control unit 439 may use an electronic signal to switch flow (for
example by providing electronic signals to one or more valves)
through a bypass (not shown) from any location in the nitrogen loop
404 (for example, from the compressor 409, from a room temperature
portion or from another warm portion of the nitrogen loop 404) to
provide warm gas to a location in the load, such as the platen 466
and/or electrostatic chuck 449, in order to warm such location
quickly for servicing. The system control unit 439 may use an
electronic signal to switch flow (for example by providing
electronic signals to one or more valves) through a bypass (not
shown) anywhere in the nitrogen loop 404 that causes the mixing of
hot gas from a warmer section of the nitrogen loop 404 (for
example, a room temperature portion of the nitrogen loop 404) with
a downstream, colder section of the nitrogen loop 404. In the case
of flow bypasses, the system control unit 439 may use an electronic
signal to control a valve (not shown) to have on/off, proportional,
or throttling operation.
[0052] In the embodiment of FIG. 4, part or all of the control
techniques implemented by system control unit 439 may be to perform
a calculation of the bypass mixing or on/off time needed to
generate the desired delivery temperature to the load, rather than,
or in addition to, performing a continuous regulation of the
desired temperature based on continuous feedback of a reading of
that temperature. Further, the system control unit 439 could
perform a calculation of how much mixing or on/off time is needed,
based on pressure and valve position rather than, or in addition
to, performing other types of control.
[0053] In the embodiment of FIG. 4, in order to control operation
of the nitrogen loop 404 and/or to control operation of the mixed
gas refrigeration system 441 in order to control the delivery
temperatures to the load (such as pre-cooling equipment
446/447/448, cold pad cryogenic interface module 465, platen 466
and/or electrostatic chuck 449), several further different possible
techniques may be used, either alone or in combination. The system
control unit 439 may control the refrigerant flow rate of either or
both of the mixed gas refrigeration system 441 or the nitrogen loop
404 by providing electronic signals to one or more valves, which
may be proportional or on/off valves. For example, such valves may
be located at the supply outputs 444, 462 of either or both of the
first and second channels 443, 450 of the mixed gas refrigeration
system 441 or at the nitrogen supply lines 451 or 459. The system
control unit 439 may change the set point temperature of the mixed
gas refrigeration system 441. The system control unit 439 may
control one or more heaters to heat one or more of the mixed gas
refrigerant or the nitrogen loop. The system control unit 439 may
regulate the speed of the compressor of the mixed gas refrigeration
system 441. The system control unit 439 may control flow through a
bypass line (for example using one or more valves) from a warmer
section of the mixed gas refrigeration system 441 (such as a warmer
heat exchanger in a cascade system, or such as a room temperature
portion of the mixed gas refrigeration system 441) to a colder
portion of the system 400. The system control unit 439 may use an
electronic signal to switch flow (for example by providing
electronic signals to one or more valves) through a bypass (not
shown) from a location in the mixed gas refrigeration system 441,
such as a defrost loop (not shown) of the system 441, to provide
warm gas to a location in the load, such as pre-cool equipment
446/447/448, in order to warm such location quickly for
servicing.
[0054] In another embodiment similar to that of FIG. 4, both the
first channel 443 of the mixed gas refrigeration system 441 and the
nitrogen supply and return lines 459, 460 may be used to improve
cool-down time of the cold pad cryogenic interface module 465,
platen 466 and/or electrostatic chuck 449. This may be done, for
example, by having separate bypass lines (not shown) from the mixed
gas refrigerant supply and return lines 444 and 445 of the first
channel 443 to the cold pad cryogenic interface module 465.
[0055] The embodiment of FIG. 4 may include devices for detecting
both under-refrigerated and over-refrigerated conditions, in a
similar fashion to those described above for FIG. 1. Instead of a
recirculating nitrogen stream 404, the system may use a stream of
argon, xenon, krypton, helium, another pure refrigerant or a mixed
refrigerant. Similar types of compressors may be used as discussed
above for FIG. 1. Heat transfer from the mixed gas refrigerant
lines 462/463 to the heat exchangers 455, 456 may be performed
using similar techniques for thermal conduction as those described
above for FIG. 1. Similar methods of flow control may be used as
discussed above for FIG. 1. Similar methods of pressure control may
be used as discussed above for the nitrogen compressor 109 of FIG.
1. Similar safety controls may be used as discussed above for FIG.
1, although some may not be necessary where vacuum insulation of
the insulated enclosure 410 is not used. Similar techniques for
control of refrigerant purity may be used as discussed above for
FIG. 1. Alternative refrigeration such as reverse Brayton may be
used to provide cooled refrigerant to both channels of a system
according to an embodiment of the invention. In addition, the
number of heat exchangers required may be varied depending on
cooling requirements and heat exchanger design.
[0056] FIG. 5 is a schematic diagram of a high throughput cooling
system 500 in accordance with an embodiment of the invention, which
is similar to the embodiment of FIG. 4 except that the insulated
enclosure 510 is integrated into mixed gas refrigeration system
541. Heat exchangers 552, 553, 555 and 556, capillary tube 558,
heater 554, adsorber 557, valves 515/516/517 are all located within
enclosure 510 in the mixed gas refrigeration system 541. The
nitrogen supply and return lines 551 and 561 are fed into the
enclosure 510 within the mixed gas refrigeration system 541; and
the nitrogen lines 559/560 to and from the load are fed from the
mixed gas refrigeration system 541 to the load. Mixed gas is
supplied at 562 to cool the nitrogen loop from mixed gas supply
lines within the mixed gas refrigeration system 541, and mixed gas
returns at 563 from having cooled the nitrogen loop. A first
channel 543 operates similarly to that of FIG. 4, using mixed gas
lines 544 and 545 to supply and return mixed gas refrigerant to and
from the customer pre-cooling equipment 546 and/or 547/548. No
second channel exiting the mixed gas refrigeration system 541 (like
second channel 450 of FIG. 4) is needed in the mixed gas
refrigeration system 541 because the mixed gas lines 562 and 563
are directed to the nitrogen loop within the mixed gas
refrigeration system 541. The electrical control box 542, nitrogen
compressor 509 and inverter 564 may be located outside of the mixed
gas refrigeration system 541. Customer equipment 567 may include a
pre-cool cryogenic interface module 546, a cold pad cryogenic
interface module 565, one or more pre-cool chambers 547 and 548, an
electrostatic chuck 549 and a platen 566. Operation may otherwise
be similar to that of the embodiment of FIG. 4.
[0057] In accordance with an embodiment of the invention, the mixed
gas refrigeration system may, for example, be an auto-refrigerating
cascade system and may include multiple heat exchangers 491 and one
or more phase separators 492 (see FIG. 4) in a mixed gas
refrigeration process. Further, the mixed gas refrigeration system
may include a branched supply line, delivering mixed refrigerant
supply to each of the mixed refrigerant supply lines 444 and 462
(see FIG. 4), and a branched return line, receiving returning mixed
refrigerant from each of the mixed refrigerant return lines 445 and
463 (see FIG. 4). Further, in the embodiments of FIGS. 4 and 5,
other types of refrigeration systems may be used in place of a
mixed gas refrigeration system. For example, a reverse Brayton
cycle or other refrigeration system may be used; and may include
branched supply and return lines to function in a similar fashion
to the supply lines 444, 462 and return lines 445, 463 of FIG. 4.
Further, the two channels 443 and 450 of the mixed gas
refrigeration system 441 may instead be implemented by two separate
mixed gas refrigeration systems, or two separate other types of
refrigeration systems.
[0058] In accordance with an embodiment of the invention, where
heat exchangers are discussed herein, different numbers of such
heat exchangers may be used depending on the system efficiency
required.
[0059] A cooling system in accordance with an embodiment of the
invention may be operated in various modes. For example, the modes
of operation may include steady state operation; standby (or
bypass) operation; startup (initial cool down from room
temperature); and shutdown (the time to warm from operating
temperature to room temperature for maintenance or other reasons).
Such modes of operation may be controlled by system control units
139 or 439, for example.
[0060] In accordance with an embodiment of the invention, a system
may be used to cool a load 493 (see FIG. 4) inside an insulated
enclosure (such as insulated enclosure 410) rather than
transferring refrigerant outside the insulated enclosure using
transfer lines. For example, such an embodiment may be useful where
biological samples are being cooled or frozen, although it may be
used with other loads as well. In addition, an embodiment according
to the invention may comprise moving a substrate or other object or
fluid to be cooled from a pre-cool chamber or other heat transfer
surface to of the load to another portion of the load, such as a
process chamber.
[0061] As used herein, the term "cryogenic" refers to the
temperature range between 233 K and 23 K (-40 C and -250 C).
[0062] The teachings of all patents, published applications and
references cited herein are incorporated by reference in their
entirety.
[0063] While this invention has been particularly shown and
described with references to example embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
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